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Fitzpatrick M.B.,University of Houston | Obara Y.,Ibaraki University | Fujita K.,Montana State University | Brown D.E.,Montana State University | And 4 more authors.
Journal of Inorganic Biochemistry | Year: 2010

We have used low-temperature (77K) resonance Raman (RR) spectroscopy as a probe of the electronic and molecular structure to investigate weak π-π interactions between the metal ion-coordinated His imidazoles and aromatic side chains in the second coordination sphere of blue copper proteins. For this purpose, the RR spectra of Met16 mutants of Achromobacter cycloclastes pseudoazurin (AcPAz) with aromatic (Met16Tyr, Met16Trp, and Met16Phe) and aliphatic (Met16Ala, Met16Val, Met16Leu, and Met16Ile) amino acid side chains have been obtained and analyzed over the 100-500cm-1 spectral region. Subtle strengthening of the Cu(II)-S(Cys) interaction on replacing Met16 with Tyr, Trp, and Phe is indicated by the upshifted (0.3-0.8cm-1) RR bands involving ν(Cu-S)Cys stretching modes. In contrast, the RR spectra of Met16 mutants with aliphatic amino acids revealed larger (0.2-1.8cm-1) shifts of the ν(Cu-S)Cys stretching modes to a lower frequency region, which indicate a weakening of the Cu(II)-S(Cys) bond. Comparisons of the predominantly ν(Cu-S)Cys stretching RR peaks of the Met16X=Tyr, Trp, and Phe variants, with the molar absorptivity ratio ε1/ε2 of σ(∼455nm)/π(∼595nm) (Cys)S→Cu(II) charge-transfer bands in the optical spectrum and the axial/rhombic EPR signals, revealed a slightly more trigonal disposition of ligands about the copper(II) ion. In contrast, the RR spectra of Met16Z=Ala, Val, Leu, and Ile variants with aliphatic amino acid side chains show a more tetrahedral perturbation of the copper active site, as judged by the lower frequencies of the ν(Cu-S)Cys stretching modes, much larger values of the ε1/ε2 ratio, and the increased rhombicity of the EPR spectra. © 2009 Elsevier Inc. Source

Uchida Y.,Ibaraki University | Urade Y.,Osaka Bioscience Institute | Mori S.,Ibaraki University | Kohzuma T.,Ibaraki University | Kohzuma T.,Frontier Research Center for Applied Atomic science
Journal of Inorganic Biochemistry | Year: 2010

The Mg2+ ion-assisted activation mechanism of the active site Tyr8 of a human hematopoietic prostaglandin D2 synthase (H-PGDS) was studied by ultraviolet resonance Raman (UVRR) spectroscopy. Addition of Mg2+ to the native H-PGDS at pH 8.0 resulted in the Y8a Raman band of Tyr8 shifting from 1615cm-1 to 1600cm-1. This large shift to lower energy of the tyrosine Y8a vibrational mode is caused by the deprotonation of the tyrosine phenol group promoted by binding of Mg2+. Upon subsequent addition of glutathione (GSH), the Mg2+/H-PGDS solution showed the Tyr8 Raman band shifted to 1611cm-1, which is 11cm-1 higher than the frequency of the Mg2+ complex of H-PGDS, but 4cm-1 lower than the Mg2+ free enzyme. These UVRR observations suggest that the deprotonated Tyr8 in the presence of Mg2+ is re-protonated by the abstraction of H+ from the thiol group of GSH, and that the re-protonated Tyr8 species forms a hydrogen bond with the thiolate anion of GSH. Density functional theory calculations on several model complexes of p-cresol were also performed, which suggested that the pKa and vibrational frequencies of the Tyr8 phenol group are affected by the degree and structure of hydration of the Tyr8 residue. © 2009 Elsevier Inc. Source

Ozeki K.,Ibaraki University | Ozeki K.,Frontier Research Center for Applied Atomic science | Aoki H.,International Apatite Co. | Masuzawa T.,Ibaraki University
Bio-Medical Materials and Engineering | Year: 2011

Hydroxyapatite (HA) was coated onto a titanium substrate using radio frequency magnetron sputtering. The sputtered film was crystallized using a hydrothermal treatment. The films were observed using X-ray diffractometry, field emission scanning electron microscopy (FE-SEM) and scanning transmission electron microscopy (STEM) equipped with energy dispersive X-ray spectroscopy (EDX). It was observed that the surface of the hydrothermally-treated film was covered with globular particles. The FE-SEM observations indicated that these particles were composed of columnar grains with a grain size of 20-50 nm. In the STEM cross-sectional observation of the HA-Ti interface, HA crystalline phase regions were observed, in part, in the non-crystalline phase layer of the as-sputtered film. After the hydrothermal treatment, the HA layer crystallized; the HA crystallization proceeded to a distance of 30 nm above the titanium surface. From an EDX line scan analysis, the titanium oxide layer was not observed at the HA-Ti interface of the as-sputtered film; however, in the hydrothermally-treated film, the titanium oxide layer, with a 15 nm thickness, was observed between the mixing layer and the titanium substrate. The formation of titanium oxide at the HA-Ti interface would contribute to the adhesion improvement of the sputtered film following the hydrothermal treatment. © 2011 - IOS Press and the authors. All rights reserved. Source

Ozeki K.,Ibaraki University | Ozeki K.,Frontier Research Center for Applied Atomic science | Hirakuri K.K.,Tokyo Denki University | Masuzawa T.,Ibaraki University
Applied Surface Science | Year: 2011

Many types of plastic containers have been used for the storage of food. In the present study, diamond-like carbon (DLC)/titanium oxide (TiO2) multilayer thin films were deposited on polypropylene (PP) to prevent flavour retention and to remove flavour in plastic containers. For the flavour removal test, two types of multilayer films were prepared, DLC/TiO2 films and DLC/TiO2/DLC films. The residual gas concentration of acetaldehyde, ethylene, and turmeric compounds in bottle including the DLC/TiO 2-coated and the DLC/TiO2/DLC-coated PP plates were measured after UV radiation, and the amount of adsorbed compounds to the plates was determined. The percentages of residual gas for acetaldehyde, ethylene, and turmeric with the DLC/TiO2 coated plates were 0.8%, 65.2% and 75.0% after 40 h of UV radiation, respectively. For the DLC/TiO2/DLC film, the percentages of residual gas for acetaldehyde, ethylene and turmeric decreased to 34.9%, 76.0% and 85.3% after 40 h of UV radiation, respectively. The DLC/TiO2/DLC film had a photocatalytic effect even though the TiO2 film was covered with the DLC film. © 2011 Elsevier B.V. All rights reserved. Source

Takashina A.,Ibaraki University | Unno M.,Ibaraki University | Unno M.,Frontier Research Center for Applied Atomic science | Kohzuma T.,Ibaraki University | Kohzuma T.,Frontier Research Center for Applied Atomic science
Chemistry Letters | Year: 2015

The first X-ray crystallographic study for the alkaline structure transition of cytochrome c' was performed. Precise X-ray crystal structures of acidic (pH 6.0) and alkaline (pH 10.4) iron(III) cytochrome c' from Alcaligenes xylosoxidans NCIMB 11015 (AxCyt c') were determined at 1.1 and 1.48 Å resolution, respectively. The structure of AxCyt c' at pH 10.4 provides direct evidence for the alkaline high-spin transition caused by bond length elongation between the heme iron and the axial His120 imidazole nitrogen atom. © 2015 The Chemical Society of Japan. Source

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